Monofilaments such as polyamide (PA) including nylon-6 and nylon-66, polydioxanone (PDS), poly(ethylene terephthalate) (PET), polyvinylidene fluoride (PVDF), etc. have been industrially used in various fields. In addition to those industrial applications, monofilaments have been widely used as biomaterials such as surgical sutures and meshes (non-patent document 1).
However, despite superior physical properties and strength, the monofilaments described above have been limited to be used for biomaterials due to insufficient biocompatibility and degradability. In order to overcome this problem, biodegradable polymers having ester, amide and ether functional groups have gained interests as biomaterials since the late 1960s in the field of biomedicine due to very superior biodegradability. Among them, the polyester poly(L-lactic acid) (PLLA) has been widely used due to very superior properties as a biomaterial, such as biocompatibility and biodegradability, as well as proven safety (non-patent document 2).
However, despite these many advantages of the biodegradable polymers such as polylactic acid, their use in the field of biomedicine requiring high mechanical strength has been restricted because their mechanical strength tends to lag behind that of non-degradable materials. In particular, because mechanical strength is a very important factor in the applications such as surgical suture and vascular stent, non-degradable materials with high strength have been mainly used in this fields (non-patent document 3).
Accordingly, it is important to improve mechanical strength for wide application of the biodegradable polymers in biomedical fields. In order to improve the mechanical strength of the biodegradable polymers, many processing techniques such as melt extrusion, melt drawing and injection molding have been developed thus far. However, these techniques are disadvantageous in that high temperature is necessary to process the polymers, which may cause loss of molecular weight and physical properties, or a very complicated multi-step process is necessary (non-patent documents 4, 5 and 6).